I decided to give it a go, and I was quite happy with it for most of my searches. That being said, it seems that most of the searches I do are for sites that I know already exist. First up I added del.icio.us to my browser search bar. Internet Explorer 7, has an easy way to add a search plugin for almost any site you like.
I also set it as my default. Previously that was Google.
20 minutes later, having put that activity to the back of my mind, I did my first search looking for the LibX site and was pleasantly
Search term=libx Search engine=del.icio.us
Results on the first page --> All results were relevant. And the first two were URLs that would get me precisely where I wanted to be.
There were a few other searches that day that I was very happy to be using Delicious for. Although for more esoteric topics with complexity it wasn't so great and I fell back to Google for help with those.
Of course Google does a fine job with a search like "libx" too. The first page of results are very similar to what I got with delicious. But I certainly did not need the 365,000 for libx. (0.17 seconds).
I'm not actually a del.icio.us 'user', that is I don't have an account. I prefer Connotea for various reasons. But I think I'll continue using del.icio.us in this way and see how I get on.
It may turn out that social bookmarking sites like del.icio.us will do for search/directories of the internet what Wikipedia has done for encyclopedias - leverage the huge 'workforce' of the entire web community. Will this put the human dimension back into search sites where the holy grail has been the algorithm?